The embodiments described herein relate generally to electric machines, and more specifically, to an interior permanent magnet rotor for use in an electric machine and methods of assembling the same.
Various types of electric machines include permanent magnets. For example, a brushless direct current (BLDC) motor may include a plurality of permanent magnets coupled to an exterior surface of a rotor core. Typically, the plurality of permanent magnets are coupled to the exterior surface of the rotor core using an adhesive and/or an outer retaining covering. The coupling between the permanent magnets and the rotor core must resist forces exerted on the permanent magnets during high speed rotation tending to separate the permanent magnets from the rotor core.
Permanent magnets may also be positioned within a rotor core. Such a rotor may be referred to as an interior permanent magnet rotor. Slots are formed within the rotor and magnets are inserted into the slots. The magnet slots must be larger than the magnets to allow the magnets to be inserted. However, the magnets must be secured within the slots to prevent movement of the magnets during operation of the machine. The performance of the machine depends on maintaining the magnets in a known position within the rotor. To secure the magnets in a fixed position relative to the rotor, the slots may be tapered in order to pinch the magnets. A tapered slot is difficult to implement due to the stagger from lamination to lamination and manufacturing tolerances. A permanent magnet may also be secured within a slot using an adhesive. However, adhesives have a limited life due to factors such as temperature, temperature cycling, and environmental conditions.